Potential use of chitosan nanoparticles for oral delivery of DNA vaccine in Asian sea bass (Lates calcarifer) to protect from Vibrio (Listonella) anguillarum

Oral immunization with attenuated Salmonella Typhimurium as a carrier of DNA vaccine against infectious hematopoietic necrosis virus (IHNV) in rainbow trout (Oncorhynchus mykiss)

Infectious hematopoietic necrosis virus (IHNV) is a serious pathogen in the salmonid aquaculture industry and leads to economic losses in the world. This study aimed to develop a new oral DNA vaccine designed to protect rainbow trout against infection by IHNV. Fish were administered via the oral route by the attenuated Salmonella enterica serovar Typhimurium as a carrier of pcDNA3.1-IHNG (glycoprotein (G)) plasmid for 7 days and finally, fish were challenged by 105 pfu ml-1 IHNV. The results revealed that the antigen gene was identified in different tissues of rainbow trout at 15-, 30-, and 45 days post-vaccination (dpv). Also, the recombinant vaccine elicited both an innate and specific immune response, resulting in a significant upregulation of the expression levels of ifn-1, mx-1, vig-1, igm, and igt. In addition, serum levels of neutralizing antibodies were observed to be elevated in the vaccinated fish, in contrast to the unvaccinated fish, following 30 dpv. Compared to trout that received empty S. Typhimurium, notable differences in cumulative percentage mortality were evident among the vaccinated fish. The relative percent survival (RPS) was recorded at 58.2 % for the group that received oral vaccine, while the group that received empty S. Typhimurium exhibited an RPS of 18.2 %. Therefore, our results showed that this bacterial vector can be a candidate carrier for pcDNA3.1-IHNG plasmid that may be employed to confer protection to rainbow trout against IHNV.

Vitamin E nanoparticles enhance performance and immune status of Nile tilapia

Vitamin E (VE) is an essential vitamin liposoluble antioxidant in aquatic animals that is usually lost during feed processing and digestion, whereas nano-chitosan, a polysaccharide, could protect VE. In this study, Nile tilapia (70.85 ± 0.2 g) was fed VE (100 mg/kg dry diet) and a chitosan protected-VE nanoparticle (NPs) with gradual percentages of recommended dose 25%, 50%, 75%, and 100% for 4, 6, and 8 weeks. Growth parameters total weight gain (TG), daily weight gain (DWG), and relative growth rate (RGR) were significantly and positively correlated with VENPs additions. Regardless of the addition level, the feed conversion ratio (FCR) was significantly lower in the VENP groups. Lysozyme, serum antibacterial activity, and oxidative burst activity indicated the superiority of VENPs (VENPs75 and VENPs100) in enhancing the fish's innate immunity compared to bulk VE and the control groups. Fish were experimentally challenged with pathogenic Aeromonas hydrophila; those received dietary showed a low mortality rate (MR%), about 40% compared with 70% in the control with lower re-isolation compared to the control and VE groups. VENPs could provide ascending relative protection level during the period of 4 to 8 weeks; RPL ranged from 33.3 to 42.86% (VENPs100), 16.67-42.86% (VENPs75), 0 to 28.57% (VENPs50), and 0 to 14.29% (VENPs25 and VE), respectively. Finally, this study recommended incorporating VENPs into the Nile tilapia diet at 50, 75, and 100 mg/ kg fish feed. Fish in the VENPs75 and VENPs100 groups were immune boosted, becoming less vulnerable to A. hydrophila infection.

Nanotechnology: An avenue for combating fish parasites in aquaculture system

The intensification of aquaculture in recent years has led to the rise of infectious fish diseases caused by bacteria, viruses, and parasites. Parasitic diseases, in particular, are widespread and have significant economic impacts globally. Protozoan parasites like Ichthyophthirius multifiliis and Trichodina sp., myxozoans (cnidarians), monogeneans like Dactylogyrus sp. and Gyrodactylus sp., and crustacean parasites like Argulus sp. and Lernaea cyprinacea primarily cause these diseases. Despite advancements and new technologies aimed at understanding and treating these diseases, parasites remain a major health challenge in aquaculture. Traditional antiparasitic agents face limitations, including drug resistance and negative effects on non-target organisms. Recently, nanotechnology has emerged as a novel approach in aquaculture medicine, enabling the development of effective nanoparticles against pathogenic microbes. Silver nanoparticles (AgNPs) are particularly notable for their strong antimicrobial and antiparasitic properties due to their broad mechanisms of action. Although Argulus is a highly destructive crustacean parasite that financially burdens fish farmers, applying nanoparticles to manage this infection in aquaculture is still underexplored. Therefore, this review explores recent efforts to combat parasitic diseases with AgNPs and investigates their potential parasiticidal mechanisms of action, proposing them as a novel tool that could improve the management and control of argulosis diseases. The article underscores the benefits and challenges of this technology, emphasizing its significance in fostering improved health management for sustainable aquaculture.

Advances in Vaccine Adjuvants for Teleost Fish: Implications for Aquatic Welfare and the Potential of Nanoparticle-Based Formulations

Vaccine adjuvants are crucial for reinforcing the immunogenicity of vaccines. Therefore, they are widely used in the aquaculture sector as vaccine components, facilitating the efficient prevention of infectious diseases and promoting sustainable teleost fish growth. Despite their benefits, there has been a growing concern about the potential adverse effects of vaccine adjuvants in teleost fish, connoting a valid impact on their overall health and welfare. Among the adjuvants used in aquaculture vaccinology, nanoparticle-based formulations have given rise to a promising new alternative to traditional options, such as oil-based emulsions and aluminum compounds, offering the benefit of minimizing relevant side effects. The aim of this paper was to review the current status of the adjuvants used in aquaculture, provide a description and an evaluation of their mode of action and side effects, and explore the potential use of nanoparticle formulations as adjuvants to improve the efficacy of aquaculture vaccines. By demonstrating and assessing the equilibrium between teleost fish welfare and immunological efficacy, this review presents a collective perspective that will assist in establishing a framework for the utilization of effective species-specific practices around adjuvant use in aquaculture, while also addressing the challenges of welfare-friendly immunization.

Review of current perspectives and future outlook on bacterial disease prevention through vaccination in Asian seabass (Lates calcarifer)

Asian seabass, Lates calcarifer, is an important aquatic species in mariculture. Intensive farming of this species has faced episodes of bacterial diseases, including those due to vibriosis, scale drop, and muscle necrosis disease, big belly disease, photobacteriosis, columnaris, streptococcosis, aeromoniasis, and tenacibaculosis. Vaccination is one of the most efficient, non-antibiotic, and eco-friendly strategies for protecting fish against bacterial diseases, contributing to aquaculture expansion and ensuring food security. As of now, although numerous vaccines have undergone laboratory research, only one commercially available inactivated vaccine, suitable for both immersion and injection administration, is accessible for preventing Streptococcus iniae. Several key challenges in developing vaccines for Asian seabass must be addressed, such as the current limited understanding of immunological responses to vaccines, the costs associated with vaccine production, forms, and routes of vaccine application, and how to increase the adoption of vaccines by farmers. The future of vaccine development for the Asian seabass industry, therefore, is discussed with these key critical issues in mind. The focus is on improving our understanding of Asian seabass immunity, including maternal immunity, immunocompetence, and immune responses post-vaccination, as well as developing tools to assess vaccine effectiveness. The need for an alignment of fish vaccines with state-of-the-art vaccine technologies employed in human and terrestrial animal healthcare is also discussed. This review also discusses the necessity of providing locally-produced autogenous vaccines, especially for immersion and oral vaccines, to benefit small-scale fish farmers, and the potential benefits that might be extended through changes to current husbandry practices such as the vaccination of broodstock and earlier life stages of their off-spring.

Bacterial diseases of Asian sea bass (Lates calcarifer): A review for health management strategies and future aquaculture sustainability

The advent of aquaculture has been one of the most significant shifts in world food supply during the last century. Aquaculture has rapidly expanded and become a global food industry, spurred by population expansion, increased seafood consumption, and decreased captured fisheries. Nonetheless, the exponential growth of aquaculture has emerged as a significant contributor to anthropogenic changes. Unexpectedly, the result has focused in the emergence and spread of new diseases. The Asian sea bass (Lates calcarifer) is an economically important species in aquaculture, contributing significantly to the global seafood market. However, bacterial diseases have emerged as a major concern, affecting both wild and cultured populations of this species. The most prevalent bacterial pathogens are streptococcus, vibriosis, nocardiosis, tenacibaculosis, and pot-belly disease. Therefore, this review aims to comprehensively analyze both emerging and non-emerging bacterial diseases affecting L. calcarifer and explore potential management approaches for their control. Through an extensive literature survey and critical evaluation of research findings, this review highlights the current understanding of bacterial diseases in L. calcarifer and proposes strategies for better disease management. In addition, this review looks at the rise and characteristics of aquaculture, the major bacterial pathogens of L. calcarifer and their effects, and the specific attributes of disease emergence in an aquatic rather than terrestrial context. It also considers the potential for future disease emergence in L. calcarifer due to aquaculture expansion and climate changes.

Immersion prime and oral boost vaccination with an inactivated Vibrio harveyi vaccine confers a specific immune response and protection in Asian seabass (Lates calcarifer)

Asian seabass (Lates calcarifer) holds significant economic value in fish farming in the Asia-Pacific region. Vibriosis caused by Vibrio harveyi (Vh) is a severe infectious disease affecting intensive farming of this species, for which prevention strategies by vaccination have been developed. This study investigated an alternative approach to injectable vaccination to prevent vibriosis in Asian seabass juveniles. The strategy begins with an immersion prime vaccination with a heat-inactivated Vh vaccine, followed by two oral booster doses administered at 14- and 28-days post-vaccination (dpv). Expression of five immune genes TNFα, IL1β, CD4, CD8, and IgM in the head kidney and spleen, along with investigation of anti-Vh antibody response (IgM) in both systemic and mucosal systems, was conducted on a weekly basis. The efficacy of the vaccines was assessed by a laboratory challenge test at 43 dpv. The results showed that the immunized fish displayed higher levels of mRNA transcripts of the immune genes after the immersion prime and the first oral booster dose compared to the control group. The expression levels peaked at 14 and 28 dpv and then declined to baseline at 35 and 42 dpv. Serum specific IgM antibodies were detected as early as 7 dpv (the first time point investigated) and exhibited a steady increase, reaching the first peak at 21 dpv, and a second peak at 35 dpv. Although the antibody levels gradually declined over subsequent weeks, they remained significantly higher than the control group throughout the experiment. A similar antibody response pattern was also observed in the mucosal compartment. The laboratory challenge test demonstrated high protection by injection with 1.65 × 104 CFU/fish, with a relative percent of survival (RPS) of 72.22 ± 7.86 %. In conclusion, our findings highlight the potential of an immersion prime-oral booster vaccination strategy as a promising approach for preventing vibriosis in Asian seabass.

Nanoencapsulated Aquafeeds and Current Uses in Fisheries/Shrimps: A Review

Feeds for aquaculture animals are designed to provide them with the greatest amount of nourishment they need to carry out their regular physiological activities, such as maintaining a potent natural immune system and boosting growth and reproduction. However, the problems that severely hamper this sector's ability to contribute to achieving global food security include disease prevalence, chemical pollution, environmental deterioration, and inadequate feed usage. The regulated release of active aquafeed components; limited water solubility, bioaccessibility, and bioavailability, as well as their potent odour and flavour, limit their utilisation. They are unstable under high temperatures, acidic pH, oxygen, or light. Recent advancements in nano-feed for aquaculture (fish/shrimp) have attract enormous attention due to its excellent nutritional value, defeating susceptibility and perishability. Encapsulation is a multifunctional smart system that could bring benefits of personalized medicine; minimize costs and resources in the preclinical and clinical study in pharmacology. It guarantees the coating of the active ingredient as well as its controlled release and targeted distribution to a particular area of the digestive tract. For instance, using nanotechnology to provide more effective fish/shrimps feed for aquaculture species. The review enables a perspective points on safety and awareness in aquafeeds that have been made by the advancements of nanosystem. Therefore, potential of nano-delivery system in aquafeed industry for aquaculture act as concluding remark on future directions.

Formulation of chitosan microsphere-based oral vaccine against the scuticociliate parasite Miamiensis avidus: Evaluation of its protective immune potency in olive flounder (Paralichthys olivaceus)

Miamiensis avidus is a parasitic pathogen that causes scuticociliatosis, a severe and often lethal marine infection that affects marine fishes worldwide, including olive flounder (Paralichthys olivaceus) in Korea. This parasite infects all size groups of flounder year-round, causing recurring mortalities and huge economic losses to the Korean flounder industry each year. However, few efforts have been made to implement effective remedial measures to control this parasite. Therefore, our study sought to develop a chitosan microsphere (MS)-encapsulated inactivated vaccine (IMa + chitosan) for oral delivery (adsorbed in feed) to flounder fingerlings and assess its protective efficacy at different modalities via three in vivo experimental trials. Immunisation trial-1 was conducted to determine the effective concentration of chitosan. Our findings indicated that an IMa + chitosan 0.05 % vaccine formulation was safe and effective in providing moderate protection [46.67%-53.3 % relative percent survival (RPS)] against M. avidus intraperitoneal (IP) injection challenge at two weeks post-vaccination (wpv) compared to the IMa + chitosan 0.01 % and IMa + chitosan 0.005 % vaccines (0%-13.3 % RPS) irrespective of the antigen doses. In trial-2, the IMa + chitosan 0.05 % vaccine elicited similar protective immunity (30.8%-57.1 % RPS) in olive flounder against M. avidus at varying antigen doses (high: 2.38 × 106 cells/fish; low: 1.5 × 105 cells/fish), immunisation periods (2 and 5 wpv), and challenge modes (IP injection and immersion). Furthermore, experimental trial-3 validated the use of chitosan MS as an IMa antigen carrier to improve survivability (41.7 % RPS) in the host by significantly (p < 0.05) upregulating specific anti-M. avidus antibody titres in the fish sera and mucus of the group immunised with IMa-containing chitosan MS. In contrast, non-specific immunomodulatory effects (16.7 % RPS and enhanced mucosal antibody titres) were observed in the group treated with chitosan MS without IMa. Therefore, our findings suggested that oral administration of chitosan MS (0.05 %)-encapsulated IMa vaccine is a promising immunisation strategy against M. avidus that can protect the IMa antigen from digestive degradation, facilitates its targeted delivery to the host immune organs, and helps in orchestrating protective immune induction in olive flounder, thus controlling parasite infection.

Inflammatory reaction and immune response of half-smooth tongue sole (Cynoglossus semilaevis) after infection with Vibrio anguillarum

Frequently occurred bacterial diseases have seriously affected the aquaculture industry of half-smooth tongue sole (Cynoglossus semilaevis). Notably, vibriosis, with Vibrio anguillarum as one of the causative pathogens, is the most severe bacterial disease with severe inflammatory response of the host, leading to high mortality rates. In the present study, we explored the relationship between bacterial concentrations and host mortality, inflammatory reaction, and immune response in half-smooth tongue sole after infection with V. anguillarum at different concentrations (Treatment 1, 6.4 × 105 CFU/mL; Treatment 2, 6.4 × 106 CFU/mL). The mortality of Treatment 2 (77.5%) was significantly higher than that of Treatment 1 (10%), corresponding with bacterial concentrations. Although the number of deaths varies, intensive deaths were observed within 24 h post infection (hpi) in both bacterial concentration groups. Histopathological analyses revealed that fish tissues were most severely damaged at 24 or 48 hpi, and Treatment 2 was more severe than Treatment 1. A qRT-PCR-based detection method with virulence factor gene empA was established to quantify the bacterial loads in various tissues, and the bacterial loads were the highest at 24 hpi in Treatment 2, and at 48 hpi in Treatment 1. Additionally, the expression levels of complement genes (C5a, C3, C5, and C6), inflammatory factors (IL-1β, TNF-α, and IL-10), and other immune-related genes (jak2, NF-κB1, stat3, and tlr3) were increased in various tissues after infection in both treatment groups, with most genes being most expressed at 24 or 48 hpi, and expression levels of inflammatory factors in Treatment 2 were higher than those in Treatment 1. Moreover, the expression of C5a was positively correlated with that of proinflammatory cytokines in both bacterial concentration groups. According to the results of this study, 24-48 hpi was a key node for early vibriosis detection and intervention. Compared with the low mortality of Treatment 1, the mass death of fish in Treatment 2 was suggested to be caused by uncontrolled excessive inflammatory reaction induced by the overactivation of complement system, especially C5a. We believe these results could provide theoretical basis for prevention, evaluation, and treatment of vibrio disease in tongue sole aquaculture, and lay a solid foundation for future functional analyses.

Repurposing chitin-rich seafood waste for warm-water fish farming

The pisciculture industry has grown multi-fold over the past few decades. However, a surge in development and nutrient demand has led to the establishment of numerous challenges. Being a potential solution, chitosan has gained attention as a bio nanocomposite for its well-acclaimed properties including biodegradability, non-toxicity, immunomodulatory effects, antimicrobial activity, and biocompatibility. This biopolymer and its derivatives can be transformed into various structures, like micro and nanoparticles, for various purposes. Consequently, with regards to these properties chitin and its derivatives extend their application into drug delivery, food supplementation, vaccination, and preservation. This review focuses on the clinical advancements made in fish biotechnology via chitosan and its derivatives and highlights its prospective expansion into the pisciculture industry-in particular, warm-water species.

Oral vaccination for sustainable disease prevention in aquaculture-an encapsulation approach

The prevalence of infectious diseases in the aquaculture industry and a limited number of safe and effective oral vaccines has imposed a challenge not only for fish immunity but also a threat to human health. The availability of fish oral vaccines has expanded recently, but little is known about how well they work and how they affect the immune system. The unsatisfactory efficacy of existing oral vaccinations is partly attributable to the antigen degradation in the adverse gastrointestinal environment of fishes, the highly tolerogenic gut environment, and inferior vaccine formulation. To overcome such challenges in designing: an easier, cost-efficient, and effective vaccination method, several encapsulation methods are being adopted to safeguard antigens from the intestinal atmosphere for their immunogenic functions. Oral vaccination is easily degraded by gastric acids and enzymes before reaching the immunological site; however, this issue can be solved by encapsulating antigens in poly-biodegradable nanoparticles, transgenic designed bacteria, plant systems, and live feeds. To enhance the immunological impact, each antigen delivery method operates at a different level. Utilizing nanotechnology, it has been possible to regulate vaccination parameters, target particular cells, and lower the antigen dosage with potent nanomaterials such as chitosan, poly D,L-lactic-co-glycolic acid (PLGA) as vaccine carriers. Live feeds such as Artemia salina can be utilized as bio-carrier, owing to their appropriate size and non-filter feed system, through a process called bio-encapsulation. It ensures the protection of antigens over the fish intestine and ensures complete uptake by immune cells in the hindgut for increased immune response. This review comprises recent advances in oral vaccination in aquaculture in terms of an encapsulation approach that can aid in future research.

Efficacy of Chitosan-PLGA encapsulated trivalent oral vaccine against viral haemorrhagic septicemia virus, Streptococcus parauberis, and Miamiensis avidus in olive flounder (Paralichthys olivaceus)

The present study was conducted to assess the protective efficacy of a trivalent oral vaccine containing chitosan-PLGA encapsulated inactivated viral haemorrhagic septicemia virus (VHSV), Streptococcus parauberis serotype I and Miamiensis avidus antigens, followed by its oral (incorporated in feed) administration to olive flounder (Paralichthys olivaceus) fingerlings for a period of 15-consecutive days. After 35 days of initial vaccination, three separate challenge studies were conducted at the optimal temperature of the targeted pathogens using an intraperitoneal injection route. RPS analysis revealed moderate protection in the immunized group against all the three pathogens viz., VHSV (53.30% RPS), S. parauberis serotype-I (33.30% RPS), and M. avidus (66.75% RPS), as compared to the respective non-vaccinated challenge (NVC) control group. In addition, the immunized fish demonstrated significantly (p < 0.05) higher specific antibody titres in serum and significant (p < 0.05) upregulation in the transcript levels of immune genes of Igs (IgM, IgT, pIgR), TLRs (TLR 2, TLR 7), cytokines (IL-1β, IL-8) and complement pathway (C3) in the mucosal and systemic tissues than those of NVC control fish, suggesting orchestration of pathogen-specific host immune responses thereby favouring its combativeness against the three pathogens. The expression dynamics of IFN-γ, Mx, caspase 3 genes post VHSV challenge; IFN-γ, TLR 2, caspase 1 genes post S. parauberis serotype I challenge and CD-8α, IL-10, TNF-α genes post M. avidus challenge further substantiates the efficacy of the vaccine in stimulating antiviral, antibacterial and antiparasitic immune responses in the host resulting in their better survival. The findings from the present study reflect that the formulated trivalent oral vaccine incorporating VHSV, S. parauberis serotype I and M. avidus antigens can be a promising prophylactic strategy to prevent the associated disease outbreaks in olive flounder.

Saponin and chitosan-based oral vaccine against viral haemorrhagic septicaemia virus (VHSV) provides protective immunity in olive flounder (Paralichthys olivaceus)

Production losses of olive flounder (Paralichthys olivaceus) have increased owing to viral haemorrhagic septicaemia virus (VHSV) infection. In this study, we determined safe concentrations of orally administered saponin and chitosan by analysing serum enzyme (AST/ALT) levels as biochemical markers of hepatic injury. Furthermore, we demonstrated the efficacy, duration of protection, and safety of saponin and chitosan-based vaccines with inactivated VHSV (IV). Oral administration of saponin, chitosan, and their combination did not induce fish mortality at all tested concentrations (0.29, 1.45, and 2.9 mg/g of fish body weight/day) 10 days after administration. However, AST level was high at a dose >0.29 mg/g of fish body weight/day. Both saponin and chitosan were found to be safe and acceptable for vaccination studies at a dose of 0.29 mg/g of fish body weight/day. Administration of IV alone did not induce protection at 2 and 4 weeks post vaccination (wpv). Olive flounders administered saponin + IV and chitosan + IV vaccines had higher immunity against VHSV with relative percentage survival (RPS) of 12.5-7.5% and 0-20.1%, respectively; however, additional immunisation with combination of saponin + chitosan + IV clearly enhanced the protection with RPS values of 10-15%, 26.7%, 42.9%, and 37.5% at 4, 8, 12, and 20 wpv, respectively. Although the RPS value of oral immunisation was not comparable to that of injectable vaccines, the manufacturing process is simple and oral administration causes less stress to juvenile fish. To investigate the development of a protective immune response, olive flounder were re-challenged with VHSV (10^7.8 TCID₅₀/fish) at 70 days postinfection; 100% of the previously unexposed fish died, whereas 80-100% of the previously immunised fish survived. Our results showed the possibility of developing preventive measures against VHSV using saponin and chitosan-based oral vaccines with inactivated virus.

Attachment and in vitro transfection efficiency of an anti-rabies Chitosan-DNA nanoparticle vaccine

In Mexico, urban rabies has been reduced during the last decade thanks to intensive canine control and vaccination campaigns; however, rabies transmitted by wild animals, especially by bats, has been increasing due to vampire bats feeding on livestock. Vampire bat populations has been controlled by culling with vampiricides, reducing indiscriminately other bat species. Hence, bat vaccination for rabies offers an alternative for culling. Nevertheless, available rabies vaccines are not suitable for their use in wildlife from emerging countries. This project presents an alternative for the use of plasmid vaccines using bio-nanotechnology, to create low-cost and accessible vaccines. To accomplish this goal, chitosan nanoparticles were synthesized by ionic gelation and conjugated by coacervation with a pDNA rabies vaccine to test their attachment efficiency. Also, the conjugate was functionalized with Protoporphyrin IX and Folic acid as biomarkers. The nanoparticles complex was characterized by ultraviolet visible spectroscopy, infrared spectroscopy, transmission electron microscopy, dynamic light scattering, and the Z potential was obtained. In vitro tests were performed on cell viability and transfection. The nanoparticles possessed a low polydispersity, a mean size of 118.5 ± 13.6 nm and a Z potential of 17.3 mV. The attachment efficiency was of 100% independent of pDNA added. In contrast to functionalized nanoparticles which showed a max attachment efficiency of 99.6% dependent of pDNA concentration and the method of functionalization. The conjugate did not influence the viability and they improved the transfection efficiency. Results suggest that these nanoparticles are easy to prepare, inexpensive, and exhibit potential for plasmid delivery as it improves transfection efficiency of pDNA vaccines.

Nano and Microparticles as Potential Oral Vaccine Carriers and Adjuvants Against Infectious Diseases

Mucosal surfaces are the first site of infection for most infectious diseases and oral vaccination can provide protection as the first line of defense. Unlike systemic administration, oral immunization can stimulate cellular and humoral immune responses at both systemic and mucosal levels to induce broad-spectrum and long-lasting immunity. Therefore, to design a successful vaccine, it is essential to stimulate the mucosal as well as systemic immune responses. Successful oral vaccines need to overcome the harsh gastrointestinal environment such as the extremely low pH, proteolytic enzymes, bile salts as well as low permeability and the low immunogenicity of vaccines. In recent years, several delivery systems and adjuvants have been developed for improving oral vaccine delivery and immunogenicity. Formulation of vaccines with nanoparticles and microparticles have been shown to improve antigen stability, availability and adjuvanticity as well as immunostimulatory capacity, target delivery and specific release. This review discusses how nanoparticles (NPs) and microparticles (MPs) as oral carriers with adjuvant characteristics can be beneficial in oral vaccine development.

In vitro evaluation of novel (nanoparticle) oral delivery systems allow selection of gut immunomodulatory formulations

Oral delivery is the most convenient way to vaccinate cultured fish, however it is still problematic, primarily due to a lack of a commercially valid vaccine vehicle to protect the antigen against gastric degradation and ensure its uptake from the intestine. With the goal of advancing the potential to vaccinate orally, this study evaluates a novel silicon nanoparticle-based vehicle (VacSaf carrier). Aeromonas salmonicida antigens were formulated with the VacSaf carrier using different preparation methods to generate dry powder and liquid formulations. Twelve formulations were first subjected to an in vitro evaluation where the A. salmonicida bacterin conjugated to VacSaf carriers were found superior at inducing pro-inflammatory cytokine expression in primary leucocyte cultures and the macrophage/monocyte cell line RTS-11 compared with A. salmonicida bacterin alone. This was especially apparent after exposure to acid conditions to mimic stomach processing. One formulation (FD1) was taken forward to oral delivery using two doses and two administration schedules (5 days vs 10 days, the latter 5 days on, 5 days off, 5 days on), and the transcript changes of immune genes in the intestine (pyloric caeca, midgut and hindgut) and spleen were evaluated by qPCR and serum IgM was measured by ELISA. The VacSaf carrier alone was shown to be safe for use in vivo, in that no side-effects were seen, but it did induce expression of some cytokines, and may have value as an oral adjuvant candidate. The FD1 bacterin formulation was effective at inducing a range of cytokines associated with innate and adaptive immunity, mainly in the pyloric caeca, compared to A. salmonicida bacterin alone (which had almost no effect), and confirms the immune competence of this gut region following appropriate oral vaccination. These results reveal that in vitro screening of formulations for oral delivery has value and can be used to assess the most promising formulations to test further.

Ecotoxicity evaluation of polymeric nanoparticles loaded with ascorbic acid for fish nutrition in aquaculture

Background

Ascorbic acid (AA) is a micronutrient essential for the mechanisms of reproduction, growth, and defense in fish. However, the biosynthesis of this micronutrient does not occur in fish, so it must be supplied with food. A difficulty is that plain AA is unstable, due to the effects of light, high temperature, and oxygen, among others. The use of nanoencapsulation may provide protection and preserve the physicochemical characteristics of AA for extended periods of time, decreasing losses due to environmental factors.

Method

This study evaluated the protective effect of nanoencapsulation in polymeric nanoparticles (chitosan and polycaprolactone) against AA degradation. Evaluation was made of the physicochemical stability of the nanoformulations over time, as well as the toxicological effects in zebrafish (Danio rerio), considering behavior, development, and enzymatic activity. For the statistical tests, ANOVA (two-way, significance of p < 0.05) was used.

Results

Both nanoparticle formulations showed high encapsulation efficiency and good physicochemical stability during 90 days. Chitosan (CS) and polycaprolactone (PCL) nanoparticles loaded with AA had mean diameters of 314 and 303 nm and polydispersity indexes of 0.36 and 0.28, respectively. Both nanosystems provided protection against degradation of AA exposed to an oxidizing agent, compared to plain AA. Total degradation of AA was observed after 7, 20, and 480 min for plain AA, the CS nanoparticle formulation, and the PCL nanoparticle formulation, respectively. For zebrafish larvae, the LC₅₀ values were 330.7, 57.4, and 179.6 mg/L for plain AA, the CS nanoparticle formulation, and the PCL nanoparticle formulation, respectively. In toxicity assays using AA at a concentration of 50 mg/L, both types of nanoparticles loaded with AA showed lower toxicity towards the development of the zebrafish, compared to plain AA at the same concentration. Although decreased activity of the enzyme acetylcholinesterase (AChE) did not affect the swimming behavior of zebrafish larvae in the groups evaluated, it may have been associated with the observed morphometric changes, such as curvature of the tail.

Conclusions

This study showed that the use of nanosystems is promising for fish nutritional supplementation in aquaculture. In particular, PCL nanoparticles loaded with AA seemed to be most promising, due to higher protection against AA degradation, as well as lower toxicity to zebrafish, compared to the chitosan nanoparticles. The use of nanotechnology opens new perspectives for aquaculture, enabling the reduction of feed nutrient losses, leading to faster fish growth and improved sustainability of this activity.

Graphic Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-021-00910-8.

Delivery of selenium using chitosan nanoparticles: Synthesis, characterization, and antioxidant and growth effects in Nile tilapia (Orechromis niloticus)

This study aimed to elucidate the effects of selenium-loaded chitosan nanoparticles used as a dietary supplement on Nile tilapia (Oreochromis niloticus) antioxidant and growth responses. First, chitosan-based nanoparticles containing selenium (Se) were synthesized using the ionotropic gelation method and their physicochemical characteristics, controlled release profile, and antioxidant activity properties were investigated. Thereafter, the effects on glutathione peroxidase and antioxidant activities (by radical scavenging activity), growth, and whole-body composition of Nile tilapia were evaluated when they were fed with Se-loaded chitosan nanoparticles and compared with other selenium dietary supplements. Se-loaded chitosan nanoparticles showed high entrapment efficiency (87%), spherical shape, smooth surface, and broad size distribution. The controlled release of Se consisted of an initial burst followed by a gradual release over 48 h. Se-loaded nanoparticles presented significantly higher antioxidant activity compared to free Se. A 60-day feeding trial was conducted to compare the effects of supplementing different dietary Se sources, including selenomethionine (as organic source), sodium selenite (as inorganic source), and Se-loaded chitosan nanoparticles (Se-Nano and Se-Nano x1.5) on antioxidant and growth responses of Nile tilapia. A basal diet without Se supplementation was used as the control. The dietary supplementations with different Se sources (free and encapsulated selenium) lead to significant improvements in final weight and feed efficiency of Nile tilapia fingerlings. However, dietary treatments did not affect whole-body protein and lipid content. Diets containing Se-Nano and Se-Nano x1.5 were more effective than sodium selenite and selenomethionine in preventing oxidative stress and improving antioxidant activity in Nile tilapia. Overall, Se-loaded nanoparticles presented a great potential as an efficient source for delivering dietary Se to Nile tilapia, directly affecting the growth performance, feed efficiency, oxidative stress, and antioxidant activity of this species.

Nano-scale applications in aquaculture: Opportunities for improved production and disease control

Aquaculture is the fastest growing food-production sector and is vital to food security, habitat restoration and endangered species conservation. One of the continued challenges to the industry is our ability to manage aquatic disease agents that can rapidly decimate operations and are a constant threat to sustainability. Such threats also evolve as microbes acquire resistance and/or new pathogens emerge. The advent of nanotechnology has transformed our approach to fisheries disease management with advances in water disinfection, food conversion, fish health and management systems. In this review, several nano-enabled technology successes will be discussed as they relate to the challenges associated with disease management in the aquaculture sector, with a particular focus on fishes. Future perspectives on how nanotechnology can offer functional approaches for improving disinfection and innovating at the practical space of early warning systems will be discussed. Finally, the importance of "safety by design" approaches to the development of novel commercial nano-enabled products will be emphasized.

Advantages and prospective challenges of nanotechnology applications in fish cultures: a comparative review

Applications of nanotechnology in fish cultures have participated in getting over various difficulties that hinder fish productivity. They can achieve growth performance after adding some important minerals and vitamins in the form of nano-feed supplements like selenium, zinc, iron, and vitamin C. Also, they have an important role in reproduction, and fish medicine as antimicrobial, drug delivery, nano-vaccination, and rapid disease diagnosis. Moreover, their roles in water remediation and purification, and fish packaging are documented. On the other hand, some nanoparticles exhibit toxic effects on living organisms, which return to their tiny size, high reactivity, and permeability. They can alter many physiological functions and cause cytotoxicity, DNA damage, and histopathological changes. Also, nanotechnology applications cause new secondary pollutants to be introduced into the environment that can negatively affect fish health and the surrounding living organisms. So, in spite of the promising applications of nanotechnology to fulfill high growth performance and pathogen-free fish, there are a lot of debates about the potential toxicity of nanomaterials, their reactivity with the surrounding environment, and bioaccumulation. The present review aims to elucidate and discuss various advantages and challenges of nanotechnology applications in fish cultures. Also, it points to green nanotechnology as a promising alternative to chemical ones.

A review article on nanotechnology in aquaculture sustainability as a novel tool in fish disease control

In recent decades, aquaculture has played a significant role in fulfilling the vast demand for animal protein requirements and consequently in food security. However, environmental contamination and disease prevalence are considered essential challenges for the sector. In this regard, new approaches have been paved in technology to deal effectively with such challenges. Among these, nanotechnology-as a novel and innovative tool-has a broad spectrum of uses and a tremendous potential in aquaculture and seafood preservation. It can provide new technologies for management of drugs as liberation of vaccines and therefore hold the assurance for civilized protection of farmed fish against disease-causing pathogens. This article presents a review of nanotechnology and its applications in aquaculture. Additionally, it gives a brief idea about the fish disease and classical ways of controlling pathogens. On the other hand, this review sheds the light on nanotechnology as a potential novel tool which may possibly enhance the management and the control of disease prevalence. Therefore, the importance of this technology to promote sustainable aquaculture has also been highlighted. Focusing on the role of selenium nanoparticles as an efficient element is discussed also in this article.

In vitro assessment of the antimicrobial efficacy of chitosan nanoparticles against major fish pathogens and their cytotoxicity to fish cell lines

Nanotechnology is an emerging avenue employed in disease prevention and treatment. This study evaluated the antimicrobial efficacy of chitosan nanoparticles (CSNPs) against major bacterial and oomycete fish pathogens in comparison with chitosan suspension. Initially, the minimum inhibitory concentrations (MIC, MIC₉₀ ) were determined and the per cent inhibition of bacterial growth was calculated. Subsequently, the minimum bactericidal concentrations (MBCs) were determined. The time-dependent disruptions of CSNP-treated pathogens were observed via transmission electron microscopy (TEM), and the effect of CSNPs on the viability of two fish cell lines was assessed. No antimicrobial effect was observed with chitosan, while CSNPs (105 nm) exhibited a dose-dependent and species-specific antimicrobial properties. They were bactericidal against seven bacterial isolates recording MBC values from 1 to 7 mg/ml, bacteriostatic against four further isolates recording MIC values from 0.125 to 5 mg/ml and fungistatic against oomycetes recording MIC₉₀ values of 3 and 4 mg/ml. TEM micrographs showed the attachment of CSNPs to the pathogenic cell membranes disrupting their integrity. No significant cytotoxicity was observed using 1 mg/ml CSNPs, while low dose-dependent cytotoxicity was elicited by the higher doses. Therefore, it is anticipated that CSNPs are able to compete and reduce using antibiotics in aquaculture.

Application of Outer Membrane Protein-Based Vaccines Against Major Bacterial Fish Pathogens in India

Aquaculture is one of the fastest-growing food-producing sectors in the world. However, its growth is hampered by various disease problems due to infectious microorganisms, including Gram-negative bacteria in finfish aquaculture. Disease control in aquaculture by use of antibiotics is not recommended as it leads to antibiotic residues in the final product, selection, and spread of antibiotic resistance in the environment. Therefore, focus is on disease prevention by vaccination. All Gram-negative bacteria possess surface-associated outer membrane proteins (OMPs), some of which have long been recognized as potential vaccine candidates. OMPs are essential for maintaining the integrity and selective permeability of the bacterial membrane and play a key role in adaptive responses of bacteria such as solute and ion uptake, iron acquisition, antimicrobial resistance, serum resistance, and bile salt resistance and some adhesins have virulence attributes. Antigenic diversity among bacterial strains even within the same bacterial species has constrained vaccine developments, but OMPs that are conserved across serotypes could be used as potential candidates in vaccine development, and several studies have demonstrated their efficacy and potential as vaccine candidates. In this review, we will look into the application of OMPs for the design of vaccines based on recombinant proteins, subunit vaccines, chimeric proteins, and DNA vaccines as new-generation vaccine candidates for major bacterial pathogens of fish for sustainable aquaculture.

Chitosan-Based Drug Delivery System: Applications in Fish Biotechnology

Chitosan is increasingly used for safe nucleic acid delivery in gene therapy studies, due to well-known properties such as bioadhesion, low toxicity, biodegradability and biocompatibility. Furthermore, chitosan derivatization can be easily performed to improve the solubility and stability of chitosan-nucleic acid polyplexes, and enhance efficient target cell drug delivery, cell uptake, intracellular endosomal escape, unpacking and nuclear import of expression plasmids. As in other fields, chitosan is a promising drug delivery vector with great potential for the fish farming industry. This review highlights state-of-the-art assays using chitosan-based methodologies for delivering nucleic acids into cells, and focuses attention on recent advances in chitosan-mediated gene delivery for fish biotechnology applications. The efficiency of chitosan for gene therapy studies in fish biotechnology is discussed in fields such as fish vaccination against bacterial and viral infection, control of gonadal development and gene overexpression and silencing for overcoming metabolic limitations, such as dependence on protein-rich diets and the low glucose tolerance of farmed fish. Finally, challenges and perspectives on the future developments of chitosan-based gene delivery in fish are also discussed.

Comparative immunohistological study on using capsaicin, piperine, and okadaic acid for the transepithelial passage of the inactivated viral and bacterial vaccines in fish

The practical difficulty of parenteral application of fish vaccines against devastating fish diseases diverted the interest toward oral vaccination. Search for effective methods to enhance the oral uptake of viral and bacterial vaccines is continuing. The current research focus on a new role of mucosal fish vaccine adjuvants inducing the antigen uptake by enhancing vascularity or increasing intestinal permeability. Some inflammatory substances cause reversible pathology to the intestinal epithelium, which could be employed for the transepithelial passage of vaccine particles. The natural inflammatory substances used were capsaicin, piperine, and okadaic acid as 1 mg, 2 mg, and 1 μg/fish, respectively. Two inactivated vaccines were used as antigens to test the effect of these inflammatory substances in two different fish hosts. Tested vaccines were inactivated redspotted grouper nervous necrosis virus vaccine in sevenband grouper (Epinephelus septemfasciatus) and inactivated Edwardsiella tarda vaccine in red sea bream (Pagrus major) fish models. The inflammatory substances and each vaccine were anally intubated to fish. Capsaicin proved to be effectively aiding the transepithelial passage of vaccine particles more than piperine, while okadaic acid had no detectable effect.

Use of silver nanoparticles to control Vibrio fluvialis in cultured angelfish Pterophyllum scalare

Nanoparticles have multiple applications, among which is their use as antimicrobial agents in aquaculture. The objective of this work was to determine the antibacterial effect of silver nanoparticles (AgNPs) against Vibrio fluvialis in cultured angelfish Pterophyllum scalare. AgNPs were synthetized through chemical reduction and characterized by UV-visible and infrared spectroscopy. Particle size ranged from 60 to 170.8 nm, and scanning electron microscopy revealed cubic and spherical forms. A minimal inhibitory concentration of 222.5 ppm was determined, as well as inhibition halos between 8.66 and 14.3 mm. Inhibition of V. fluvialis growth was observed upon contact with AgNPs. An 88% survival of infected fish was obtained when treated with AgNPs, in contrast to 100% mortality of fish that were not treated. No damage to internal or external organs was observed in fish exposed to AgNPs. We conclude that AgNPs exert an antimicrobial effect against V. fluvialis, and thus represent a new alternative to control diseases caused by this microorganism in P. scalare culture.

Induction of Gonadal Development in Protogynous Grouper with Orally Delivered FSH DNA

The availability of sexually mature fish often dictates the success of its captive breeding. In this study, we induced reproductive development in juvenile protogynous tiger grouper through oral administration of a plasmid (p) containing an engineered follicle-stimulating hormone (FSH). An expression construct (pcDNA3.1) was designed to express a single-chain FSH consisting of giant grouper FSH β-subunit and glycoprotein subunit-α (CGα), linked by the carboxy-terminal peptide (CTP) sequence from the human chorionic gonadotropin (hCG). Single oral delivery of pFSH encapsulated in liposome and chitosan to tiger grouper yielded a significant increase in plasma FSH protein level after 4 days. Weekly pFSH feeding of juvenile tiger groupers for 8 weeks stimulated ovarian development as indicated by a significant increase in oocyte diameter and progression of oocytes to cortical alveolar stage. As the pFSH treatment progressed from 20 to 38 weeks, female to male sex change was initiated, characterized by oocyte regression, proliferation of spermatogonial cells, and occurrence of spermatogenic cysts. It was also associated with significantly lower mRNA expression of steroidogenic genes (cyp11b, cyp19a1a, and foxl2) and basal plasma levels of sex steroid hormones 17β-estradiol (E₂), testosterone (T), and 11-ketotestosterone (11KT). Results suggest that pFSH stimulates ovarian development up to cortical alveolar stage and then initiates sex change in tiger grouper. These findings significantly contribute to our knowledge on the role of FSH in the development of protogynous hermaphroditic fish. This study is the first to demonstrate induction of reproductive development in fish through oral delivery of plasmid gonadotropin.

Recent progress in biomedical applications of chitosan and its nanocomposites in aquaculture: A review

Chitosan nanoparticles (CSNPs) are the nanostructures of chitosan biopolymer which is derived from chitin polysaccharide, the main component of crustacean shells. Chitosan is a biocompatible, nontoxic and biodegradable polymer soluble in acidic solutions and easily excreted from kidneys. It is widely used in medical and pharmaceutical applications including artificial matrices for tissue engineering, drug transport, targeted drug delivery and protein or gene delivery. The antimicrobial activities of chitosan and CSNPS against different bacterial, fungal and viral pathogens made them valuable for several biological applications including food preservation purposes. In addition, they have immunomodulatory effects on fish and crustaceans providing direct positive impact on aquaculture and fish farming industry. Sustained release of some bioactive ingredients such as hormones, vitamins, nutrients and antioxidants has improved the biological activities of fish. Furthermore, CSNPs have recently been employed to diagnose fish diseases. In this review, we present the medical and biological applications of chitosan and CSNPs on aquatics to provide an update on recent advances and the potential for further advanced applications for aquaculture in the future.

Nanoencapsulation of inactivated-viral vaccine using chitosan nanoparticles: Evaluation of its protective efficacy and immune modulatory effects in olive flounder (Paralichthys olivaceus) against viral haemorrhagic septicaemia virus (VHSV) infection

Viral haemorrhagic septicaemia virus (VHSV), a (-) ssRNA virus belonging to the genus Novirhabdovirus of rhabdoviridae family, is the aetiological agent of viral haemorrhagic septicaemia (VHS) disease which causes huge economic losses in farmed olive flounder (Paralichthys olivaceus) and significant mortalities among several other marine fish species in Korea, Japan, and China. Previously, we developed an inactivated vaccine viz., formalin-inactivated VHSV mixed with squalene as adjuvant which was effective in conferring protective immunity (58-76% relative percentage survival) against VHSV but the mode of administration was intraperitoneal injection which is not feasible for small sized fingerling fish. To overcome this limitation, we presently focused on replacing the injection route of vaccine delivery by oral and immersion routes. In this context, we encapsulated the inactivated VHSV vaccine with chitosan nanoparticles (CNPs-IV) by water-in-oil (W/O) emulsification method. After encapsulation, two sets of in vivo vaccination trials were conducted viz., preliminary trial-I and final trial-II. In preliminary trial-I, olive flounder fingerlings (10.5 ± 1.7 g) were vaccinated with CNPs-IV by different delivery strategies involving oral and immersion routes (single/booster dose) followed by challenge with VHSV (1 × 10⁶ TCID₅₀ virus/fish) to evaluate an effective method amongst different applied delivery strategies. Subsequently, a final trial-II was conducted to better understand the immune mechanism behind the efficacy of the employed delivery strategy and also to further improvise the delivery mechanism with prime-boost (primary immersion and oral boosting) combination in order to improve the transient anti-VHSV response in the host. Evaluation of RPS analysis in trial-I revealed higher RPS of 46.7% and 53.3% in the CNPs-IV (immersion) and CNPs-IV (immersion/immersion) groups, respectively compared to 0% RPS in the CNPs-IV (oral) group and 20% RPS in the CNPs-IV (oral/oral) group when calculated against 100% cumulative mortality percentage in the NVC (non-vaccinated challenged) control group, whereas, in the trial-II, RPS of 60% and 66.6% were obtained for CNPs-IV (immersion/immersion) and CNPs-IV (immersion/oral) groups, respectively. In addition, specific (anti-VHSV) antibody titre in the fish sera, skin mucus and intestinal mucus of the immunized groups were significantly (p < 0.05) enhanced following vaccination. Furthermore, CNPs-IV immunized fish showed significant (p < 0.05) upregulation of different immune gene transcripts (IgM, IgT, pIgR, MHC-I, MHC-II, IFN-γ, and Caspase3) compared to control, in both the systemic (kidney) and mucosal (skin and intestine) immune compartments of the host post immunization as well as post challenge. To conclude, mucosal immunization with CNPs-IV vaccine can orchestrate an effective immunization strategy in organizing a coordinative immune response against VHSV in olive flounder thereby exhibiting higher protective efficacy to the host with minimum stress.

Current Advances in Chitosan Nanoparticles Based Drug Delivery and Targeting

Nanoparticles (NPs) have been found to be potential targeted and controlled release drug delivery systems. Various drugs can be loaded in the NPs to achieve targeted delivery. Chitosan NPs being biodegradable, biocompatible, less toxic and easy to prepare, are an effective and potential tool for drug delivery. Chitosan is natural biopolymer which can be easily functionalized to obtain the desired targeted results and is also approved by GRAS (Generally Recognized as Safe by the United States Food and Drug Administration [US FDA]). Various methods for preparation of chitosan NPs include, ionic cross-linking, covalent cross-linking, reverse micellar method, precipitation and emulsion-droplet coalescence method. Chitosan NPs are found to have plethora of applications in drug delivery diagnosis and other biological applications. The key applications include ocular drug delivery, per-oral delivery, pulmonary drug delivery, nasal drug delivery, mucosal drug delivery, gene delivery, buccal drug delivery, vaccine delivery, vaginal drug delivery and cancer therapy. The present review describes the formation of chitosan, synthesis of chitosan NPs and their various applications in drug delivery.

A DNA Vaccine Encoding the VAA Gene of Vibrio anguillarum Induces a Protective Immune Response in Flounder

Vibrio anguillarum is a pathogenic bacterium that infects flounder resulting in significant losses in the aquaculture industry. The VAA protein previously identified in flounder is associated with a role in immune protection within these fish. In the present study, a recombinant DNA plasmid encoding the VAA gene of V. anguillarum was constructed and its potential as a DNA vaccine, to prevent the infection of V. anguillarum in flounder fish, investigated. We verified the expression of the VAA protein both in vitro in cell lines and in vivo in flounder fish. The protective effects of pcDNA3.1-VAA (pVAA) were analyzed by determination of the percentage of sIgM⁺, CD4-1⁺, CD4-2⁺, CD8β⁺ lymphocytes, and the production of VAA-specific antibodies in flounder following their immunization with the DNA vaccine. Histopathological changes in immune related tissues, bacterial load, and relative percentage survival rates of flounder post-challenge with V. anguillarum, were all investigated to assess the efficacy of the pVAA DNA vaccine candidate. Fish intramuscularly immunized with pVAA showed a significant increase in CD4-1⁺, CD4-2⁺, and CD8β⁺ T lymphocytes at days 9, 11, and 14 post-vaccination, reaching peak T-cell levels at days 11 or 14 post-immunization. The percentage of sIgM⁺ lymphocytes reached peak levels at weeks 4–5 post-immunization. Specific anti-V. anguillarum or anti-rVAA antibodies were induced in inoculated fish at days 28–35 post-immunization. The liver of vaccinated flounder exhibited only slight histopathological changes compared with a significant pathology observed in control immunized fish. Additionally, a lower bacterial burden in the liver, spleen, and kidney were observed in pVAA protected fish in response to bacterial challenge, compared with pcDNA3.1 vector control injected fish. Moreover, the pVAA vaccine confers a relative percentage survival of 50.00% following V. anguillarum infection. In summary, this is the first study indicating an initial induction of the T lymphocyte response, followed by B lymphocyte induction of specific antibodies as a result of DNA immunization of flounder. This signifies the important potential of pVAA as a DNA vaccine candidate for the control of V. anguillarum infection.

Application of marine-derived polysaccharides as immunostimulants in aquaculture: A review of current knowledge and further perspectives

The use of antibiotics in the feeds of cultivable aquatic animals has been generally practised to reduce infectious diseases as well as to improve the survival and growth. In recent years, many countries ban to aquatic animals due to the use of large amount of antibiotics and chemotherapies, thus alternative novel strategies are need to promote the growth of aquatic animals and control the pathogens. Dietary supplementation of marine-derived polysaccharides (MDPs) is one of the potential substitutes for antibiotics in aquatic animal feeds. Recently, the use of dietary MDPs in the aquaculture animals has been focused with much interest. In aquaculture, MDPs are used as prebiotic substance which is mostly accepted as a nutritional component for improving the growth performance and health conditions. Hence, present review is a comprehensive and an updated collection of available research reports on different MDPs (alginate, fucoidan, carrageenan, laminarin, ulvan, galactan, agar, chitin and chitosan), route of administration, dosage and applications for improving aqua feeds with emphasis on its effects on growth, biochemical indices, immune response, gut microbiota and disease resistance of aquaculture animals. This review describes the sustainability of global aquaculture production by providing a best alternative to harmful antibiotics, thereby meeting the emerging consumer demand for antibiotic-free aquatic food products.

Vibriosis in Fish: A Review on Disease Development and Prevention

Current growth in aquaculture production is parallel with the increasing number of disease outbreaks, which negatively affect the production, profitability, and sustainability of the global aquaculture industry. Vibriosis is among the most common diseases leading to massive mortality of cultured shrimp, fish, and shellfish in Asia. High incidence of vibriosis can occur in hatchery and grow-out facilities, but juveniles are more susceptible to the disease. Various factors, particularly the source of fish, environmental factors (including water quality and farm management), and the virulence factors of Vibrio, influence the occurrence of the disease. Affected fish show weariness, with necrosis of skin and appendages, leading to body malformation, slow growth, internal organ liquefaction, blindness, muscle opacity, and mortality. A combination of control measures, particularly a disease-free source of fish, biosecurity of the farm, improved water quality, and other preventive measures (e.g., vaccination) might be able to control the infection. Although some control measures are expensive and less practical, vaccination is effective, relatively cheap, and easily implemented. In this review, the latest knowledge on the pathogenesis and control of vibriosis, including vaccination, is discussed.

Feed pellets containing chitosan nanoparticles as plasmid DNA oral delivery system for fish: In vivo assessment in gilthead sea bream (Sparus aurata) juveniles

The aim of this study was the assessment of preloaded feed pellets as a delivery system for plasmid DNA (pDNA), with the purpose of evaluating the potential administration of DNA vaccines orally in aquacultured fish. Pellets were made up by usual feed ingredients, which were mixed with chitosan nanoparticles entrapping a model plasmid (pCMVβ) expressible in eukaryotic cells before being elaborated. The plasmid is characterized by the insertion of the reporter gene lacZ, encoding for the bacterial enzyme β-galactosidase (β-gal). The possible in vivo expression of the exogenous gene was measured in different fish tissues of gilthead sea bream (Sparus aurata) juveniles by two different procedures. On the one hand, the activity of the enzyme β-gal was detected and quantified in muscle, liver and intestine; on the other, specific IgM against β-gal antigen was titrated in blood samples. Intramuscular (i.m.) injection of equal amounts of plasmid was also carried out for the purpose of comparison with oral administration. The expression of the reporter gene was detected in fish tissues following both oral and i. m. administration of pDNA up to 60 days. However, organ distribution of the gene expression was more evident after oral (β-gal activity measured in gut, liver and muscle) than after parenteral administration (restricted to adjacent muscle tissues). In agreement, specific IgM titration indicated that humoral immune response was more intense and sustained throughout the experimental period after oral than after i. m. delivery of equal amounts of pDNA. These results suggest that feed pellets containing chitosan nanoparticles might enable efficient oral delivery of pDNA, a fact that might imply valuable applications in terms of on-farm mass immunization purposes, especially with regard to DNA-based vaccines and small size fish, in which i. m. administration remains unfeasible.

Nanoparticle mucoadhesive system as a new tool for fish immune system modulation

Recently, chitosan-based nanoparticles with mucoadhesive properties emerged as a strategy for mucosal drug release. This study aimed to characterize the interaction of mucoadhesive system chitosancoated PLGA nanoparticles (NPMA) with fish external mucus. NP suspensions with fluorescent probe were prepared and characterized by size, polydispersity, zeta potential and pH measures. In post-exposure fish were observed an increase in fluorescence imaging over time and it was significantly influenced by NPMA concentration. We also observed the main predominance the fluorescence in the spleen, followed by liver, gill and other tissues. The use of mucoadhesive nanocarriers becomes an alternative for administration of drugs and immunomodulators in immersion systems since the nanosystem can adhere to the mucosal surface of the fish with little residual effect in the water.

Nanoconjugation of bicistronic DNA vaccine against Edwardsiella tarda using chitosan nanoparticles: Evaluation of its protective efficacy and immune modulatory effects in Labeo rohita vaccinated by different delivery routes

DNA-based immunization has proven to be an effective prophylactic measure to control aquatic animal diseases. In order to improve the efficiency of vaccine against fish pathogen, novel delivery mechanism needs to be adopted. In the present study we nanoconjugated the previously constructed DNA vaccine (pGPD + IFN) with chitosan nanoparticles (CNPs) by complex coacervation process. After construction of the vaccine, an in vivo vaccination trial was conducted in which 2 groups of rohu (L. rohita) fingerlings were vaccinated with CNPs-pGPD + IFN, one group by oral route (incorporated in feed for 14 days) and the other by immersion route (primary and booster immunised), whereas, a third group was intramuscularly (I/M) injected (initial and booster immunised) with naked pGPD + IFN and subsequently challenged with E. tarda (8.7 × 10⁴ CFU/fish) at 35-day post initial vaccination. The protective immune responses were determined in terms of relative percentage survival (RPS), specific antibody production, non-specific immune response, expression kinetics of immune-related genes and pathological manifestation. Evaluation of RPS analysis revealed that CNPs-pGPD + IFN groups recorded highest RPS (81.82% and 72.73% in oral and immersion vaccinated fish group respectively) while the naked pGPD + IFN injected group showed 63.62% RPS when compared with 55% cumulative mortality of control group. In addition, NBT, myeloperoxidase activity, serum lysozyme activity and specific antibody titre in case of CNPs-pGPD + IFN groups showed higher activities during all the time points. Furthermore, CNPs-pGPD + IFN groups showed significant (p < 0.05) upregulation of different immune gene transcripts (IgHC, iNOS, TLR22, NOD1 and IL-1β) in three immunologically important tissues post immunization (both primary and booster dose) as well as after challenge. Thus, from this study, we can conclude that oral or immersion vaccination with CNPs-pGPD + IFN can orchestrate an effective immunisation strategy in organizing a coordinative immune response against E. tarda in L. rohita exhibiting minimum stress to the host with maximum efficacy.

Recombinant Hsp33 and OmpC protein can serve as promising divalent vaccine with protection against Vibrio anguillarum and Edwardsiella tarda in flounder (Paralichthys olivaceus)

Vibrio anguillarum and Edwardsiella tarda are severe aquaculture pathogens shared similar epidemiological characteristics and susceptible to flounder (Paralichthys olivaceus). In our previous studies, recombinant(r) protein heat shock protein 33 (rHsp33) from V. anguillarum and outer membrane protein C (rOmpC) from E. tarda were proved to have protection against V. anguillarum and E. tarda, respectively. In this paper, the cross protection of rHsp33 against E. tarda and rOmpC against V. anguillarum, and the protection of divalent vaccine candidate (rHsp33 + rOmpC, rHC) against both V. anguillarum and E. tarda were evaluated. RHC, rHsp33, and rOmpC were vaccinated to flounder, respectively, and the percentages of surface immunoglobulin-positive (sIg+) cells in peripheral blood lymphocytes (PBLs), serum IgM, specific antibodies against V. anguillarum or E. tarda, specific antibodies against rHsp33, rOmpC or rHC, the expression of immune-related genes and relative percent survival (RPS) against V. anguillarum or E. tarda were measured. The results showed that: RHC could induced the enhancement of sIg + cells and high levels of specific antibodies against both V. anguillarm and E. tarda; Also a significant increase of specific antibodies against rHsp33, rOmpC or rHC, and up-regulation of gene expression of CD3, CD4-1, CD4-2, CD8α, CD8β and IgM in spleen, head-kidney, and hindgut, RPS of 70 ± 3.45% against V. anguillarum and 60 ± 1.48% against E. tarda, respectively. In addition, rHsp33 induced specific antibodies against E. tarda and rOmpC, and had a RPS of 43.3 ± 3.73% against E. tarda; rOmpC could evoke specific antibodies against V. anguillarum and rHsp33, and had a RPS of 44 ± 1.27% against V. anguillarm; The results demonstrated that there was cross protection of rHsp33 against E. tarda and rOmpC against V. anguillarum, rHC as a divalent vaccine can induce significant immune response and efficient protection against both E. tarda and V. anguillarum in flounder.

Preparation, characterization and evaluation of the immune effect of alginate/chitosan composite microspheres encapsulating recombinant protein of Streptococcus iniae designed for fish oral vaccination

Streptococcus iniae has caused serious harm to the fish farming industry in recent years. Vaccination is a potential approach for preventing and controlling disease, being oral vaccination the most suitable vaccination route in fish. Alginate and chitosan microspheres have been widely used as controlled release systems for oral vaccination in fish. In this study, we prepared and characterized alginate/chitosan composite microspheres encapsulating the recombinant protein serine-rich repeat (rSrr) of S. iniae. We evaluated effect of these microspheres on the immune system of channel catfish. The microsphere preparation conditions were optimized by Response Surface Method and target microspheres were obtained under 1.68% alginate (w/v), the W/O ratio 3.6:7.4 (liquid paraffin with 4% Span 80, v/v) with stirring at 1000 rpm, 9.64% CaCl₂ (w/v) and 0.95% chitosan (w/v) with an encapsulation efficiency of 92.38%. The stability and safety of rSrr-microspheres were evaluated in vitro and in vivo, respectively. Furthermore, compared with control group, oral vaccination with rSrr-microspheres induced higher serum antibody titers, higher lysozyme activity, higher total protein and higher expression of immune-related genes, and resulted in higher relative percent survival (RPS) with the value of 60% for channel catfish against S.iniae infection. Our results thus indicate that alginate/chitosan microspheres encapsulating rSrr can be used as oral vaccine for channel catfish, providing efficient immunoprotection against S. iniae infection.

Delivery of viral recombinant VP28 protein using chitosan tripolyphosphate nanoparticles to protect the whiteleg shrimp, Litopenaeus vannamei from white spot syndrome virus infection

The VP28 gene of white spot syndrome virus was amplified by PCR using gene specific primer set and cloned into pRSET B vector to produce recombinant VP28 (r-VP28) in E. coli GJ1158. The chitosan tripolyphosphate nanoparticles (CS/TPP) were prepared by ionic gelation process and characterized. The purified r-VP28 protein was encapsulated by CS/TPP nanoparticles. The encapsulation efficiency of CS/TPP nanoparticles was found to be 84.8% for r-VP28 protein binding with CS/TPP nanoparticles. The in vitro release profile of encapsulated r-VP28 was determined after treating with protease and chitosanase. The different types of feed were formulated and named as normal feed with PBS, Feed A coated with crude r-VP28, Feed B with purified r-VP28 and Feed C with CS/TPP encapsulated r-VP28 (Purified). Tissue distribution and clearance of r-VP28 at different time intervals were examined in shrimp fed with different types of feed by ELISA and the results showed the presence of r-VP28 protein in different organs. Various immunological parameters were assessed in experimental shrimp. The mRNA expression of five immune-related genes was analysed by qPCR in order to investigate their response to all types of feed in shrimp. A cumulative percentage mortality was also recorded in treated shrimp challenged with WSSV.

Steroidogenic acute regulatory protein (StAR) gene expression construct: Development, nanodelivery and effect on reproduction in air-breathing catfish, Clarias batrachus

Steroidogenic acute regulatory protein (StAR) is responsible for the relocation of cholesterol across mitochondrial membrane in vertebrates and is, therefore, a key factor in regulating the rate and timing of steroidogenesis. In the present study, we developed chitosan nanoparticle (CNP) conjugated StAR gene construct (CNP-pcDNA4-StAR) in a eukaryotic expression vector, pcDNA4/HisMax A. CNPs of 135.4nm diameter, 26.7mV zeta potential and 0.381 polydispersity index were used for conjugation. The loading efficiency (LE) of pcDNA4-StAR construct with CNPs was found to be 86%. After the 24h of intramuscular injection, the CNP-pcDNA4-StAR plasmid could be detected from testis, brain, kidney and muscle tissues of Clarias batrachus. The transcript levels of important reproductive genes viz. cyp11a1, cyp17a1, 3β-hsd, 17β-hsd and cyp19a1 in CNP-pcDNA4-StAR treated group were initially low up to 24h, but significantly increased subsequently up to 120h. In naked pcDNA4-StAR treated group, the mRNA level of 3β-hsd, 17β-hsd and cyp19a1 increased initially up to 24h, while cyp11a1 and cyp17a1 increased up to 48h and then started declining. Similar results were obtained for 11-Ketotestosterone and 17β-estradiol. The results indicate relatively long lasting effects of nano-conjugated construct compared to the construct alone. Furthermore, the histopathology of gonads and liver authenticates its possible role in the gonadal development in fish without any adverse effect.

An oral chitosan DNA vaccine against nodavirus improves transcription of cell-mediated cytotoxicity and interferon genes in the European sea bass juveniles gut and survival upon infection

Vaccines for fish need to be improved for the aquaculture sector, with DNA vaccines and the oral administration route providing the most promising improvements. In this study, we have created an oral chitosan-encapsulated DNA vaccine (CP-pNNV) for the nodavirus (NNV) in order to protect the very susceptible European sea bass (Dicentrarchus labrax). Our data show that the oral CP-pNNV vaccine failed to induce serum circulating or neutralizing specific antibodies (immunoglobulin M) or to up-regulate their gene expression in the posterior gut. However, the vaccine up-regulated the expression of genes related to the cell-mediated cytotoxicity (CMC; tcrb and cd8a) and the interferon pathway (IFN; ifn, mx and ifng). In addition, 3 months after vaccination, challenged fish showed a retarded onset of fish death and lower cumulative mortality with a relative survival of 45%. Thus, we created a chitosan-encapsulated DNA vaccine against NNV that is partly protective to European sea bass juveniles and up-regulates the transcription of genes related to CMC and IFN. However, further studies are needed to improve the anti-NNV vaccine and to understand its mechanisms.